1. Field Of The Invention
The present invention relates to an electronic watch having an isochronous period generator for supplying an electrical output signal defining a succession of isochronous periods and, more particularly, to a period generator which is adjustable to a desired value of sufficient accuracy that at most a predetermined absolute adjustment error is tolerated.
2. Description Of The Prior Art
Presently, known electronic reference isochronous period generators intended to control time-measuring instruments comprise, typically, an oscillator generally operating at high frequency, that is, with short periods, this frequency being divided electronically in order to obtain a lower frequency the period of which corresponds to the isochronous interval sought, for instance, to activate time indicating means. The best known electronic time base generators of this kind make use of a quartz reference oscillator, the frequency of which is divided by a series of binary dividing stages. Be means of feed back connections or of pulse suppressing means the dividers may be caused to operate at any cycle different from 2.sup.n (n=integer), but generally the high base frequency preferably is so adjusted as to be equal to the isochronous period being sought multiplied by n.sup.2, where n is the number of binary stages of the divider. Regardless of the method being used, the division ratio is generally fixed and the base high frequency must be exactly adjusted with respect to this division ratio.
A quartz oscillator provides extreme frequency accuracy, but in view of the very high quality factor Q of quartz, its frequency only can be adjusted with considerable difficulties by acting upon an element in the oscillator unless it be within an extremely narrow control range. Therefore, quartz must be cut with extreme accuracy in order to give it a natural resonance frequency extremely close to the required frequency for the desired reference isochronous period, and with the division ratio of the divider taken into account. This very high precision makes quartz costly. Furthermore, attention must be paid that the inherent aging of any oscillator shall not shift the quartz frequency outside the very narrow range within which adjustment is feasible, so that steps must be taken to provide that the quartz be only very slightly subjected to aging effects. Otherwise, subsequent compensation of aging variation becomes impossible. Again this adds to the costs involved in the use of quartz or other similar electrical oscillators that might also be used.
In U.S. Pat. No. 3,646,371 to Flad there is disclosed an electronic timing circuit which is resettable to adjust for deviations of the oscillator frequency from its nominal value. This patent is not concerned with a timing circuit for a watch, but rather a timing circuit for a rocket, the use of which is entirely different and which is subject to contingencies which are entirely different from those of a watch. Furthermore, in this known timing circuit of Flad there is no true isochronal period within the sense of the present invention since the period which one can set and reset in advance in Flad is in fact measured only once in autonomous operation whereupon the rocket explodes with the timing device.
The disclosure of Swiss Pat. No. 534,913, the specification (provisional patent) of which was published on May 15, 1972, also may be compared with the present invention. This Swiss patent discloses a quartz timer in which there is a frequency divider with an adjustable division ratio, this ratio being memorized in coded form in a memory. This Swiss patent is concerned only with a timer and not with a watch, and mentions miniaturization of the timer.
It may be thought that a combination of the disclosure of the Swiss Pat. No. 534,913 and the disclosure of the U.S. Pat. No. 3,646,371 might place an electronic watch in accordance with the present invention within the scope of one of ordinary skill in the art. However, this combination itself would raise a number of problems and it is entirely clear that those elements of the present invention which could be derived from the above-mentioned two patents could not be produced, or in any event could not be produced advantageously, without first of all having solved certain problems for which these patents provide no solution. Of primary concern is the fact that the setting or readjusting arrangement of the device in accordance with U.S. Pat. No. 3,646,371, first, uses galvanic connections (for instance "ground" 18 and "setter power" 24) and, secondly, requires that various other items of information also be transmitted by the galvanic connections (for instance "memory set" 20 and "memory reset" 22). Such a system with galvanic connections would probably make it possible to apply without great difficulty the resetting method disclosed by the U.S. Flad patent to a horological device of large dimensions and/or of a type such that the presence of connecting terminals is not disturbing. On the other hand, this arrangement would not make it possible -- or then in all cases only in a very complicated and inconvenient manner and at the cost of a very large number of difficulties in construction -- to apply this method to watches, for instance wristwatches, in view of, in particular, the very compact and closed structure of a watch and the practical impossibility of providing in it means for galvanic connection with the outside.
If the use of conventional wireless transmission means for a daily rate readjusting arrangement for a watch were contemplated, the transmissions would have to be at least of the multiple channel type, over several parallel channels, or by modulation and coding. This would enormously complicate the construction of the emitting and receiving transmission devices, in view of the very small dimensions of a watch and also the tolerance of the mutual positioning of the receiving members arranged within the watch and the emitting members located outside the watch, which tolerance would have to be very wide in order to make inconvenient manipulations unnecessary.